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stl_pair.h (__may_be_null_pointer_init): New. 

2008-10-18  Douglas Gregor  <doug.gregor@gmail.com>

	* include/bits/stl_pair.h (__may_be_null_pointer_init): New.
	(pair::pair): Eliminate the redundant pair(U1&&, U2&&) constructor.
	Add lvalue pair<U1, U2> constructor to handle non-const pair lvalues.
	Remove the old variadic constructor, and instead provide several
	variadic constructors that avoid failing when attempting to
	initialize a pointer from a null pointer constant.
	* testsuite/20_util/pair/moveable.cc (test3): Add new tests with
	initialization of pointers from the null pointer constant.

From-SVN: r141214
This commit is contained in:
Douglas Gregor 2008-10-18 23:02:17 +00:00 committed by Paolo Carlini
parent 3cdf0c6237
commit c393ec5a87
3 changed files with 138 additions and 9 deletions
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11
libstdc++-v3/ChangeLog
View File

@ -1,3 +1,14 @@
2008-10-18 Douglas Gregor <doug.gregor@gmail.com>
* include/bits/stl_pair.h (__may_be_null_pointer_init): New.
(pair::pair): Eliminate the redundant pair(U1&&, U2&&) constructor.
Add lvalue pair<U1, U2> constructor to handle non-const pair lvalues.
Remove the old variadic constructor, and instead provide several
variadic constructors that avoid failing when attempting to
initialize a pointer from a null pointer constant.
* testsuite/20_util/pair/moveable.cc (test3): Add new tests with
initialization of pointers from the null pointer constant.
2008-10-17 Paolo Carlini <paolo.carlini@oracle.com>
* include/bits/forward_list.tcc (forward_list<>::

91
libstdc++-v3/include/bits/stl_pair.h
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@ -65,8 +65,35 @@
#include <bits/move.h> // for std::move / std::forward, std::decay, and
// std::swap
#ifdef __GXX_EXPERIMENTAL_CXX0X__
#include <type_traits>
#endif
_GLIBCXX_BEGIN_NAMESPACE(std)
#ifdef __GXX_EXPERIMENTAL_CXX0X__
// A trait that determines whether the initialization of a T from
// arguments of type Args could possibly be the initialization of a
// pointer from a null pointer constant.
template<typename, typename...>
struct __may_be_null_pointer_init
: public false_type { };
template<typename _Tp, typename _Up>
struct __may_be_null_pointer_init<_Tp*, _Up>
: public integral_constant<bool,
(is_integral<typename remove_reference<_Up>::type>::value
|| is_enum<typename remove_reference<_Up>::type>::value)>
{ };
template<typename _Class, typename _Tp, typename _Up>
struct __may_be_null_pointer_init<_Tp _Class::*, _Up>
: public integral_constant<bool,
(is_integral<typename remove_reference<_Up>::type>::value
|| is_enum<typename remove_reference<_Up>::type>::value)>
{ };
#endif
/// pair holds two objects of arbitrary type.
template<class _T1, class _T2>
struct pair
@ -89,10 +116,12 @@ _GLIBCXX_BEGIN_NAMESPACE(std)
: first(__a), second(__b) { }
#ifdef __GXX_EXPERIMENTAL_CXX0X__
template<class _U1, class _U2>
pair(_U1&& __x, _U2&& __y)
: first(std::forward<_U1>(__x)),
second(std::forward<_U2>(__y)) { }
// Omitted the following constructor, which appears in the C++0x
// working paper but is redundant with the variadic constructors
// below.
//
// template<class _U1, class _U2>
// pair(_U1&& __x, _U2&& __y);
pair(pair&& __p)
: first(std::move(__p.first)),
@ -111,12 +140,56 @@ _GLIBCXX_BEGIN_NAMESPACE(std)
: first(std::move(__p.first)),
second(std::move(__p.second)) { }
// http://gcc.gnu.org/ml/libstdc++/2007-08/msg00052.html
template<class _U1, class _Arg0, class... _Args>
pair(_U1&& __x, _Arg0&& __arg0, _Args&&... __args)
// This constructor is required so that lvalue pairs don't get
// pushed to the variadic constructor below.
template<class _U1, class _U2>
pair(pair<_U1, _U2>& __p)
: first(const_cast<const pair<_U1, _U2>&>(__p).first),
second(const_cast<const pair<_U1, _U2>&>(__p).second) { }
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 811. pair of pointers no longer works with literal 0
// Variadic constructor. The enable_if makes sure that we won't
// try to initialize a pointer from an integral type, which
// needs to be handled by a different constructor that will
// convert a null pointer constant to that pointer type. See
// library issue 767.
template<class _U1, class... _Args,
class _Checker
= typename enable_if<
(!__may_be_null_pointer_init<_T1, _U1>::value
&& !__may_be_null_pointer_init<_T2, _Args...>::value),
void>::type>
pair(_U1&& __x, _Args&&... __args)
: first(std::forward<_U1>(__x)),
second(std::forward<_Arg0>(__arg0),
std::forward<_Args>(__args)...) { }
second(std::forward<_Args>(__args)...) { }
// Variadic constructor. The enable_if makes sure that the
// second argument isn't going to try to initialize a pointer
// from an integral type. However, T1 may be a pointer whose
// argument was a null pointer constant.
template<class... _Args,
class _Checker
= typename enable_if<
!__may_be_null_pointer_init<_T2, _Args...>::value,
void>::type>
pair(const _T1& __x, _Args&&... __args)
: first(__x),
second(std::forward<_Args>(__args)...) { }
// Constructor typically used when T2 is a pointer and the
// second argument was a null pointer constant. The enable_if
// makes sure that the first argument isn't going to try to
// initialize a pointer from an integral type.
template<class _U1,
class _Checker
= typename enable_if<
!__may_be_null_pointer_init<_T1, _U1>::value,
void>::type>
pair(_U1&& __x, const _T2& __y)
: first(std::forward<_U1>(__x)),
second(__y) { }
pair&
operator=(pair&& __p)

45
libstdc++-v3/testsuite/20_util/pair/moveable.cc
View File

@ -64,9 +64,54 @@ test2()
r.second.size() == 2 && p.second.size() == 0);
}
struct X {
explicit X(int, int) { }
private:
X(const X&) = delete;
};
struct move_only {
move_only() { }
move_only(move_only&&) { }
private:
move_only(const move_only&) = delete;
};
void
test3()
{
int *ip = 0;
int X::*mp = 0;
std::pair<int*, int*> p1(0, 0);
std::pair<int*, int*> p2(ip, 0);
std::pair<int*, int*> p3(0, ip);
std::pair<int*, int*> p4(ip, ip);
std::pair<int X::*, int*> p5(0, 0);
std::pair<int X::*, int X::*> p6(mp, 0);
std::pair<int X::*, int X::*> p7(0, mp);
std::pair<int X::*, int X::*> p8(mp, mp);
std::pair<int*, X> p9(0, 1, 2);
std::pair<int X::*, X> p10(0, 1, 2);
std::pair<int*, X> p11(ip, 1, 2);
std::pair<int X::*, X> p12(mp, 1, 2);
std::pair<int*, move_only> p13(0);
std::pair<int X::*, move_only> p14(0);
std::pair<int*, move_only> p15(0, move_only());
std::pair<int X::*, move_only> p16(0, move_only());
std::pair<move_only, int*> p17(move_only(), 0);
std::pair<move_only, int X::*> p18(move_only(), 0);
}
int
main()
{
test1();
test2();
test3();
}